Numerous systems have been disclosed for blending two or more fluids during the dispensing of a fluid product. Such systems are used quite often in a service station environment where it is desired to dispense a plurality of different grades or octane levels of gasoline products by blending a high octane level product with a low octane level product to create one or more mid-level octane products. Blending systems offer the potential for savings stemming from reduced storage capacity requirements both at the service station and the bulk plant level. One example of such a system is that disclosed in U.S. Pat. No. 4,876,653 ("the '653 patent"), the contents of which are incorporated herein by reference. The '653 patent discloses a system for blending low and high octane gasoline with the fuel flow rate in each of two fuel flow paths being under individual closed loop control. The system includes an algorithm for comparing the ratio of the actual accumulated volumes of the low octane to the high octane fuel relative to a statistically determined ratio of the ideal volume of the low to high octane fuel for the total accumulated volume of the sum of the volumes of the fuels at a given time. The system provides a very exact blend relative to a pre-selected blend ratio.
Each of the previous systems in this area, including that disclosed in the '653 patent, are based on an important underlying assumption: that the octane levels in the low and high octane fuel storage tanks are correct. Typically, it is assumed that the low octane blend component has an octane of about 86 to 87 and that the high octane component has an octane level of about 92 to 93. Given the octane variability inherent in the refining process, many oil companies add 1/2 to 1 point of octane to each of the blending components to ensure that each level of blended product meets or exceeds the posted octane rating. This extra octane is referred to as "octane give away" and can be quite costly. Thus, it would be desirable to eliminate the need to boost octane levels of the blending components to ensure that a proper blended product is provided to the customer.
Another potential problem with current octane blending systems is that they have no provision to detect the delivery of an incorrect octane level product in either the high or low level octane blending component storage tanks. That is, if a low octane product is dropped into both the low octane storage tank and to the high octane storage tank, it may not be possible to deliver a proper octane blend under any circumstances. Similarly, if a high octane product is delivered into the low octane product storage tank the station operator will lose an inordinate amount of money due to the "octane give away" occurring for both the blended and the low octane level products. Even if only a partial fuel delivery is dropped into the wrong tank, it may be impossible for a correctly blended product to be created. Thus, it would be desirable to provide a system for monitoring octane levels in blending component storage tanks to alert operators that blending component octane levels are outside desired limits and thus cannot be blended to meet posted octane levels.
Previous blending systems for service station use have not incorporated the actual octane levels of the blend components into the blend control process because no satisfactory octane sensor has been available. In the past octane testing has required a great deal of time to perform using expensive laboratory equipment. Octane sensors that have been available required up to about four minutes to provide an octane reading. The advent of real time octane sensors permits octane level to be included as a control parameter for octane blending in a service station setting. An example of such a sensor is that disclosed in Clarke et al., U.S. Pat. No. 5,225,679 the content of which is incorporated herein by reference. This sensor monitors hydrocarbon-based fuel properties using a mid-IR light source to illuminate fuel in a side stream flow provided for octane monitoring. The light passing through the fuel is received by a narrow bandwidth detector. The molecules of the fuel components are excited by the mid-IR light, and the amount of absorption exhibited by these excited molecules is detected and used to identify the presence of and to quantify the volume percent of the fuel components in solution. This information may be used to determine know properties of the fuel solution to include octane levels.